Toothed chains are preferably used for transmitting power in internal combustion engines, e.g. as timing chains. Conventional toothed chains consist of alternating outer and inner chain links, the outer chain link comprising two outer plates and at least one toothed extension plate disposed centrally on joint pins. The outer plates and, optionally, also the toothed extension plates of the outer chain link are press-fitted on the joint pin. Other than the toothed extension plates, the outer plates are normally implemented as guide plates, but there are also versions in which at least one guide plate is disposed in the middle of the outer chain link, or in which outer guide plates are additionally provided, whereas the actual outer plates are also implemented as toothed plates. The individual outer chain links are interconnected by means of inner chain links, which, normally, each consist of at least two individual inner toothed plates, or stacks of inner toothed plates, the inner toothed plates of the inner chain links being pivotably arranged on the joint pins, so that each roundpin chain joint is defined by a round pin of the outer chain joint and the joint openings of the inner toothed plates of the inner chain link. Depending on the respective structural design of the toothed chain, the toothed extension plates are arranged centrally between the outer plates or more closely to one of the outer plates. It is here even possible that the toothed extension plate borders directly on the outer plates, whereas a single inner toothed plate or a stack of inner toothed plates is provided between the toothed extension plates. Depending on the requirements that have to be satisfied by the toothed chain, the inner toothed plates and the toothed extension plates may be identical, which makes production of the plate and mounting of the toothed chain simple. There are, however, also toothed chains that make use of different toothed plates for the inner toothed plates of the inner chain link and the toothed extension plates of the outer chain link.
Whereas the outer plates have openings for the joint pins, whose diameter is smaller than the diameter of the joint pins, so as to allow press fitting for the interference fit of the outer plates, the joint openings of the inner toothed plates and, optionally, of the toothed extension plates have a diameter which is slightly larger than the diameter of the joint pin so as to allow especially a pivotable mode of arrangement of the inner toothed plates of the inner chain link on the joint pin.
These and other known toothed chains are well-established for the respective case of use and have proved to be successful in operation. Nevertheless, the round joint pin is, depending on its hardness, susceptible to bending in such a conventional version of a round-pin-joint toothed chain, whereas in particular the joint opening of the inner toothed plates is subjected to wear due to the movement of the joint pin in the joint opening, especially in cases where hardened joint pins are used. In the case of conventional toothed chains these problems result in an elongation of the toothed chain due to bending of the joint pin, or in increased wear of the round-pin chain joint, and, consequently, in a limitation of the service life of the toothed chain as a whole.